Department of Animal Science, Faculty of Agriculture and Natural Resources, Arak University, 38156-88349, Arak, Iran.
Faculty of Veterinary and Agricultural Sciences, Dookie Campus, University of Melbourne, Victoria 3647, Australia.
J Dairy Sci. 2022 Feb;105(2):1115-1130. doi: 10.3168/jds.2021-21208. Epub 2022 Jan 5.
The objective of this study was to investigate the effects of milk allowances equal to 526 g/d as moderate (MOD) versus 790 g/d of milk dry matter as high (HI), and starter diets containing 18% or 23% crude protein (CP), on growth performance, blood metabolites, and purine derivative (PD) excretion in the urine of dairy calves. A total of 52 female Holstein dairy calves (40.8 kg of body weight) were randomly assigned to the experimental diets. The treatments were (1) moderate milk and 18% CP starter diet (MOD-18CP); (2) MOD and 23% CP starter diet (MOD-23CP); (3) high milk and 18% CP starter diet (HI-18CP); and (4) HI and 23% CP starter diet (HI-23CP). Calves had free access to a starter feed and water and were weaned on d 53 but remained in the study until d 73. Urine samples were collected during the preweaning period (for 6 consecutive days between d 35 and 40) and postweaning period (for 6 consecutive days between d 65 and 70) to investigate urinary excretion of PD. Starter feed intake, β-hydroxybutyrate (BHB), and blood urea concentrations were reduced; however, average daily gain (ADG) and blood glucose levels increased in calves fed HI before weaning compared with MOD. During the preweaning period, high milk feeding increased total urinary PD excretion but decreased it after weaning. The 23CP diet resulted in higher feed intake and ADG before weaning and higher excretion of allantoin and total excretion of PD compared with the 18CP diet. The HI-23CP treatment resulted in the greatest withers and hip heights at weaning and final measurement, as well as the highest preweaning blood insulin concentrations. In terms of rumen development, MOD-23CP showed the greatest benefits based on starter intake, blood BHB concentration, and urinary excretion of PD. Based on the higher urinary excretion of PD found in HI-fed calves before weaning, it is possible that milk feeding overestimates estimated microbial yield. The results suggest that feeding starters with a higher proportion of CP may help maintain a more balanced ratio of CP to ME during high milk feeding, to avoid protein deficiency due to low starter intake. When calves are fed a high milk allowance, urine excretion of PD may be misinterpreted as a measure of estimated microbial growth and rumen development; this should be considered during calculations of estimated microbial yield in milk-fed calves.
本研究旨在探讨给予奶牛中量（MOD，526g/d）和高量（HI，790g/d）牛奶干物质以及粗蛋白（CP）含量分别为 18%和 23%的犊牛开食料，对犊牛生长性能、血液代谢物和尿嘌呤衍生物（PD）排泄的影响。将 52 头荷斯坦雌性奶牛犊（体重 40.8kg）随机分配到实验日粮中。处理方式为：（1）中量牛奶和 18%CP 开食料（MOD-18CP）；（2）MOD 和 23%CP 开食料（MOD-23CP）；（3）高量牛奶和 18%CP 开食料（HI-18CP）；（4）HI 和 23%CP 开食料（HI-23CP）。犊牛可自由采食开食料和饮水，并于第 53 天断奶，但在第 73 天仍留在研究中。在哺乳期（第 35 至 40 天连续 6 天）和断奶后（第 65 至 70 天连续 6 天）收集尿液样本，以研究 PD 的尿排泄情况。与 MOD 相比，HI 可降低犊牛断奶前的开食料采食量、β-羟丁酸（BHB）和血尿素浓度，但提高 ADG 和血糖水平。在哺乳期，高量牛奶喂养增加了总 PD 尿排泄，但断奶后减少了总 PD 尿排泄。与 18%CP 日粮相比，23%CP 日粮在哺乳期前提高了采食量和 ADG，提高了尿中尿囊素和 PD 的总排泄。HI-23CP 处理在断奶和最终测量时表现出最大的肩高和髋高，以及断奶前血液胰岛素浓度最高。在瘤胃发育方面，MOD-23CP 基于开食料采食量、血 BHB 浓度和 PD 尿排泄表现出最大的益处。由于 HI 喂养的犊牛在哺乳期前 PD 尿排泄较高，因此牛奶喂养可能高估了微生物估计产量。结果表明，在高量牛奶喂养时，饲喂高比例 CP 的开食料可能有助于维持 CP 与 ME 之间更平衡的比例，以避免因开食料采食量低而导致的蛋白质缺乏。当犊牛饲喂高量牛奶时，PD 的尿排泄可能被错误地解释为估计微生物生长和瘤胃发育的衡量标准；在计算牛奶喂养犊牛的估计微生物产量时，应考虑这一点。
